18WuD2x

direct-conversion receiver • direct ground 195
Ant.
RF amp.
Mixer
Local
osc.
direct-conversion receiver
AF amp.
Speaker or
headset
is amplified, then mixed with the RF output of a
tunable local oscillator, producing an audiofrequency
(AF) beat note. The AF is amplified;
audio filtering can be added. Although the directconversion
receiver somewhat resembles the
superheterodyne type, it has no intermediatefrequency
(IF) chain, and does not normally
provide single-signal reception. Also see ZERO-
BEAT RECEPTION.
direct-coupled amplifier An amplifier in which
the output circuit of one stage is wired directly to
the input circuit of the following stage (i.e., there
is no intervening capacitor or transformer). Such
an amplifier can handle alternating-current (ac)
or direct-current (dc) signals, and has wide frequency
response.
direct-coupled transistor logic Abbreviation,
DCTL. In digital computer and switching circuits,
a logic system using only direct-coupled transistor
stages.
direct coupling Direct connection of one circuit
point to another for signal transmission (i.e.,
without intermediate capacitors or transformers).
Because coupling devices aren’t used, direct coupling
provides transmission of direct current (dc),
as well as alternating current (ac).
direct current 1. Abbreviation, dc. A current that
always flows in the same direction (i.e., the polarity
never reverses). The current might be constant,
as from a battery or a regulated power
supply; it might be pulsating, as from an unfiltered
rectifier. 2. Pertaining to current that always
flows in the same direction. 3. Descriptive
of a voltage, resistance, or other parameter under
conditions in which there is a usually constant
current that always flows in the same
direction.
direct-current amplifier An amplifier for boosting
direct-current (dc) signals, as opposed to dc voltage
signals.
direct-current bar See DC BAR.
direct-current beta See DC BETA.
direct-current block See DC BLOCK.
direct-current bus See DC BUS.
direct-current circuit breaker See DC CIRCUIT
BREAKER.
direct-current component See DC COMPONENT.
direct-current converter See DC CONVERTER.
direct-current coupling See DC COUPLING.
direct-current dump See DC DUMP.
direct-current equipment See DC EQUIPMENT.
direct-current erase head See DC ERASE HEAD.
direct-current generator See DC GENERATOR.
direct-current inverter See DC INVERTER.
direct-current leakage See DC LEAKAGE.
direct-current motor See DC MOTOR.
direct-current noise See DC NOISE.
direct-current power See DC POWER.
direct-current relay See DC RELAY.
direct-current resistance See DC RESISTANCE.
direct-current shift See DC SHIFT.
direct-current short See DC SHORT.
direct-current signaling See DC SIGNALING.
direct-current source See DC SOURCE.
direct-current transducer See DC TRANSDUCER.
direct-current transformer See DC TRANS-
FORMER.
direct-current transmission See DC TRANSMIS-
SION.
direct digital control In a digital computer, multiplexing
or time sharing among a number of controlled
loops.
direct display unit A cathode-ray-tube (CRT) peripheral
that displays data recalled from memory.
direct-distance dialing A form of telephone service
that allows dialing of long-distance numbers
without involving a human operator.
direct drive 1. Pertaining to electromechanical accessories
for electronic equipment. 2. The transmission
of power directly from a source (such as
a motor) to a driven device without intermediate
gears, belts, or clutches.
direct-drive robot A robot that uses the minimum
possible number of gears and other drive systems.
direct-drive torque motor In a positioning or
speed-control system, a servoactuator connected
directly to the driven load.
direct-drive tuning A tuning or adjusting mechanism
in which the shaft of the variable component
(such as a potentiometer or variable
capacitor) is turned directly by a knob (i.e., without
gearing, dial cable, or similar linkage).
directed number A number having direction as
well as magnitude; a vector quantity.
direct electromotive force A direct-current (dc)
voltage that does not fluctuate or pulsate.
direct emf See DIRECT ELECTROMOTIVE FORCE.
direct ground 1. A ground connection made by the
shortest practicable route. Compare INDIRECT
GROUND. 2. An earth ground.